Rights groups have called for the release of a prominent Saudi reform activist and a woman who led a rare protest last week.
The protest was staged against detentions without charge in Saudi Arabia's war against al-Qaeda militants.
Abdullah al-Hamed and Rima al-Juraish were arrested on Thursday in the town of Buraida north of Riyadh after security forces announced they found secret weapons concealed at Juraish's home.
A colleague of Juraish, who took part in a women's protest outside state security headquarters in Buraida on Monday over detentions of their husbands, announced that police planted the weapons themselves to give an acceptable explanation for the arrests.
There was reason to believe they were being held over "peaceful exercise of their right to freedom of expression,” a statement from London-based Amnesty International said.
"I am afraid that the government tries to silence me," Hamed said in May.
He was among the organizers of a reform petition this year which was highly critical of the Interior Ministry.
Hamed is the lawyer for Juraish's husband, one of 3,000 men the authorities accept are being held in detention without charge on suspicion of links to militants.
